Search

This research paper investigates new and first insights into the magnetic and magnetocaloric properties of one-dimensional (1D) cobalt ferrite CoFe2O4 (CFO) nanofibers (NFs) fabricated using a sol–gel-based electrospinning technique, focusing in particular on their behavior at low temperatures for specific applications. The microstructural, structural, magnetic, and magnetocaloric properties of the calcined CFO NFs were explored. The microstructure of the NFs, with an average diameter of 210 nm, was examined by scanning and transmission electron microscopy (SEM, TEM). The x-ray diffraction (XRD) of the CFO NFs showed a pure cubic close-packed (ccp) spinel crystalline structure with the Fd 3 ¯ m space group. The Raman spectroscopic studies further confirm the cubic inverse spinel phase. The magnetic properties were explored as a function of temperature, ranging from 10 K to 300 K, and ferromagnetic behavior was observed with the highest saturation magnetization of 75.87 emu/g and coercivity of 723 Oe at room temperature. The variation of the magnetic entropy was measured indirectly using the Maxwell approach with an increasing magnetic field. A maximum of Δ S = 1.71 J/K was reached around 32 K. At 180 K, the associated adiabatic temperature change, ΔTmax, was 0.93 K, with a large RCP value of 7.58 J/kg, which is reasonably high for the corresponding nanoparticles (NPs). This work suggests that 1D CFO NFs offer a promising route for the production of nanostructured magnetic materials, potentially impacting various electronic and electromagnetic device applications at low temperatures. [ABSTRACT FROM AUTHOR]

Multiferroic CoFe2O4–Ba0.95Ca0.05Ti0.89Sn0.11O3 composite nanofibers (CFO–BCTSn NFs) were synthesized using a sol–gel electrospinning method. Scanning electron microscopy revealed the morphology of the composites, with fiber diameters ranging from 120 to 150 nm. Transmission electron microscopy confirmed the structure of the nanofibers, while X-ray diffraction, Raman spectroscopy, and high-resolution transmission electron microscopy verified the formation of the spinel structure of CFO and the perovskite structure of BCTSn, with no additional phases detected. The magnetic properties of the CFO–BCTSn NFs were demonstrated by magnetic hysteresis loops (M-H), and piezoresponse force microscopy confirmed their piezoelectricity. Magnetoelectric coupling was evidenced by comparing the M-H hysteresis loops of electrically poled and unpoled CFO–BCTSn NFs samples. These composite nanofibers have the potential to be utilized in innovative, lead-free magnetoelectric and magnetic field sensing technologies at the nanoscale. [ABSTRACT FROM AUTHOR]

Lead-free Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) ceramic powders were synthesized using the sol–gel method. The ceramics thickness was reduced to achieve high-energy storage and large electrocaloric effect in bulk ceramics. Dielectric, ferroelectric, energy storage, and electrocaloric properties were investigated for BCZT ceramic with 400 µm. Here, pure crystalline structure and homogenous microstructure were identified by XRD analysis and SEM measurements, respectively. The dielectric measurements revealed a maximum dielectric constant associated with ferroelectric–paraelectric phase transition. The maximum of ε r ′ was 17841, around 352 K. Furthermore, the BCZT ceramic exhibited improved energy storage and electrocaloric properties. A high recoverable energy density Wrec of 0.24 J/cm3 and a total energy density Wtotal of 0.27 J/cm3 with an efficiency coefficient of ~ 88% at 423 K under an electric field of 55 kV/cm were obtained. Besides, The maximum value of ΔT = 2.32 K, the electrocaloric responsivity ζ = 0.42 K mm/kV, the refrigeration capacity RC = 4.59 J/kg and the coefficient of performance COP = 12.38 were achieved around 384 K under 55 kV/cm. The total energy density Wtotal and the temperature change ΔT were also calculated by exploiting the Landau–Ginzburg–Devonshire (LGD) theory. The theoretical results matched the experimental findings. These results suggest that the synthesized BCZT ceramic with reduced thickness could be a promising candidate for energy storage and electrocaloric applications. [ABSTRACT FROM AUTHOR]

Lead-free perovskite materials with high performance have high potential in clean energy storage applications and developments of electrocaloric devices. This work reports structural, dielectric, ferroelectric, energy storage, and electrocaloric properties near the ambient temperature in barium stannate titanate (BaTi0.89Sn0.11O3, BTS11) ceramic prepared by a sol–gel method. A single perovskite structure formation was confirmed using the X-ray diffraction analysis. Average grain size of 18.5 µm was found by the mean of the SEM micrograph with a density of 5.91 g/cm3. The multiphase coexistence at very near ambient temperature was proved using temperature-dependent micro-Raman measurements and differential scanning calorimetry. The BTS11 ceramic exhibits a high dielectric constant of 15,460 and a low dielectric loss (< 0.055) in a broad temperature range. Moreover, a high energy storage density of 122 mJ/cm3 was shown with an efficiency of 79%, a maximum value of electrocaloric temperature change (ΔT) of 0.86 K, and finally, an electrocaloric responsivity (ΔT/ΔE) of 0.24 K.mm/kV at the external electric field change of 35 kV/cm near ambient temperature. The enhanced dielectric, ferroelectric, and electrocaloric properties make BTS11 ceramics a great candidate for solid-state cooling technology and high energy storage applications near ambient temperature. [ABSTRACT FROM AUTHOR]

Structural, dielectric, ferroelectric, energy storage properties, and electrocaloric effect were studied in lead-free ceramic Ba0.95Ca0.05Ti0.89Sn0.11O3 (BCTSn) elaborated by the sol–gel method. Phase purity structure was confirmed from X-ray data using the Rietveld refinement analysis which revealed the coexistence of tetragonal (P4mm) and orthorhombic (Amm2) symmetries at room temperature. Phase transitions were detected by dielectric and differential scanning calorimetry measurements. The energy storage properties were determined from P-E hysteresis, and the electrocaloric properties were calculated indirectly via the Maxwell approach. The large value of electrocaloric temperature change of ΔT = 0.807 K obtained at a relatively small electric field of 30 kV cm−1, and the high energy storage efficiency can make BCTSn ceramic a promising candidate for environmentally friendly refrigeration and energy storage applications. [ABSTRACT FROM AUTHOR]

The effects of 2% Zr introduction in Ba0.8Ca0.2TiO3 (BCT) system on its electrical and electrocaloric properties was investigated. BCT and Ba0.8Ca0.2Zr0.02Ti0.98O3 (BCZT) ceramics synthesized by solid-state processing were crystallized in a pure perovskite phase with a group space P4mm. After Zr insertion, the enhanced dielectric constant was obtained around the Curie temperature (Tc) in BCZT ceramic (εr = 6330 at Tc = 388 K) compared to BCT ceramic (εr = 5080 at Tc = 388.6 K). Moreover, the large-signal piezoelectric coefficient (d 33 ∗) was improved from 270 to 310 pm/V in BCT and BCZT ceramics, respectively, under a moderate electric field of 25 kV/cm. The electrocaloric effect was determined via indirect and direct methods. In the indirect approach, the electrocaloric temperature change (ΔT) was calculated via Maxwell relation, and the measured ferroelectric polarization P (E, T) extracted from the P–E curves recorded at 24 kV/cm. The maximum values of ΔT = 0.68 K and the electrocaloric responsivity ζ = 0.283 K mm/kV obtained at 385 K in BCZT ceramic were found to be higher than those observed in BCT ceramic (ΔT = 0.37 K and ζ = 0.154 K mm/kV at 387 K). In the direct approach, ΔT was measured utilizing a modified high-resolution calorimeter at 14 kV/cm. As the direct method is more sensitive to the latent heat, it provided larger values for smaller applied field, i.e., ΔT = 0.474 and 0.668 K for BCT and BCZT ceramics, respectively. A significant ζ of 0.477 K mm/kV was obtained in BCZT at 385 K and 14 kV/cm that matches the values found in lead-based materials. These results suggest that BCZT lead-free ceramics could have an excellent potential to be used in solid-state refrigeration applications. [ABSTRACT FROM AUTHOR]

Lead-free Ba0.85Ca0.15Zr0.10Ti0.90O3 (BCZT) ceramics have demonstrated excellent dielectric, ferroelectric, and piezoelectric properties in comparison to lead-based materials. The synthesis of pure and crystalline BCZT nanopowders at low temperatures of 25, 80, and 160 °C was reported previously by using a sol–gel method followed by a hydrothermal route. In this study, the structural, dielectric, and ferroelectric properties of sintered BCZT ceramics at 1250 °C/10 h were investigated. XRD measurements revealed the presence of a single perovskite phase at room temperature with the coexistence of the orthorhombic and tetragonal symmetries. The increase of grain size and the ceramic density in BCZT ceramics result in an enhancement of the dielectric and ferroelectric properties of BCZT ceramics. More interestingly, the synthesis temperature of BCZT powders with high dielectric and ferroelectric properties could be decreased to a low temperature of 160 °C, which is about 1200 °C lower when compared with solid-state reaction and 840 °C lower when compared with sol–gel methods. The BCZT ceramics elaborated at 160 °C revealed excellent electrical properties (dielectric constant, dielectric loss, remnant polarization, and maximal polarization of 12,085, 0.017, 8.59 µC/cm2, and 27.21 µC/cm2, respectively) and enhanced energy performances (recovered energy density and energy efficiency of 367.2 mJ/cm3 and 67.2%, respectively). Hence, the use of low-temperature hydrothermal processing can be encouraging for the synthesis of lead-free ceramics with high dielectric and ferroelectric properties. [ABSTRACT FROM AUTHOR]

Lead-free Ba0.85Ca0.15Zr0.10Ti0.90O3 (BCZT) ceramic exhibits excellent dielectric, ferroelectric and piezoelectric properties at the morphotropic phase boundary (MPB). Previously, we demonstrated that the use of the anionic surfactant sodium dodecyl sulfate (SDS, NaC12H25SO4) could enhance the dielectric properties of BCZT ceramic using surfactant-assisted solvothermal processing [1]. In the present study, structural, dielectric, ferroelectric properties, as well as electrocaloric effect and energy storage performances of this BCZT ceramic were thoroughly investigated. X-ray diffraction (XRD) measurements revealed the presence of single perovskite phase at room temperature with the coexistence of orthorhombic and tetragonal symmetries. In-situ Raman spectroscopy results confirmed the existence of all phase transitions from rhombohedral through orthorhombic and tetragonal to cubic symmetries when the temperature varies as reported in undoped-BaTiO3. Evolution of energy storage performances with temperature have been investigated. BCZT ceramic exhibits a high energy storage efficiency of ~ 80% at 120 °C. In addition, the electrocaloric responsivity was found to be 0.164 × 10−6 K·m/V at 363 K. [ABSTRACT FROM AUTHOR]

This study is devoted to the physicochemical and mineralogical characterizations of palygorskite from Marrakech High Atlas, Morocco. The raw clay and its Na-saturated <2 μm fraction were characterized using chemical, structural, and thermal analytical techniques. Measurements of specific surface area and porous volume are reported. The clay fraction was found to be made up of 95 % of palygorskite and 5 % of sepiolite. An original feature of this palygorskite is its deficiency in zeolitic HO. The half-cell structural formula of its dehydrated form was determined on the basis of 21 oxygens to be (SiAl)(MgAlFeTi $$ \square_{1} $$)(CaNaK)O, while the hydrated form could be formulated as (SiAl)(MgAlFeTi)(CaNaK)O(OH)(OH)·2.43 HO. These formulas show that the (Al+Fe)/Mg ratio is around 0.84, revealing a pronounced dioctahedral character. Further, inside its octahedral sheet, it was determined that the inner M sites are occupied by vacancies, whereas the M sites are shared between 90 % of trivalent cations (78 % for Al and 22 % for Fe), 7.5 % of Mg, and 2.5 % of Ti, all of them linked to 1.94 of structural hydroxyls. The two remaining Mg by half-cell occupy edge M sites and are coordinated to 3.88 molecules of OH. Channels of this palygorskite are deficient in zeolitic HO since they contain only 2.43 HO molecules. A correlation was found between these results and the observation of very intense and well-resolved FTIR bands arising from dioctahedral domains (mainly AlOH, FeOH, and AlFeOH) along with very small responses from a trioctahedral domain (MgOH). Accordingly, a schematic representation of the composition of the octahedral sheet was proposed. The cation exchange capacity, specific surface area, and total pore volume were also assessed to be ca. 21.2 meq/100 g, 116 m/g, and 0.458 cm/g, respectively. [ABSTRACT FROM AUTHOR]